This invention relates generally to electro-fluid servo systems and methods, and particularly to such systems wherein a relatively weak electric signal is tranformed to a relatively strong mechanical force.
Electro-fluid control valves are usually employed in instances where remote control of mechnical acton is needed, and where space, weight, and power limitations prohibit using the same form of energy for control as is used for the prime mover of mechanical action. For example, in modern aircraft, including jet aircraft and missile type aircraft, fluid devices are used to move the airfoil control surfaces. Most applications for electro-fluid control devices use only liquid hydraulic fluid (electro-hydraulic), and occur in instances where not all of the above enumerated restrictions are encountered simultaneously. In some larger systems, the control logic may be hydraulic, and built into the valve itself, eliminating the need for external sensing/control devices. The usual type of known electro-hydraulic control valve may involve the use of a dual hydraulic amplifier system where a separate lower pressure hydraulic system causes a spool valve to shift, and the spool valve releases or closes off a higher pressure hydraulic source then causing the higher pressure hydraulic source to be used in a piston. The requirement for a secondary hydraulic system is cumbersome, and if provision must stll be made for the electric signal to first control the weak hydraulic system, the result is a bulky, three tier system. Also, using a weak hydraulic system for control of a stronger hydraulic system will limit the actuator valve of the secondary hydraulic system to a weaker pressure drop with which to move the primary high pressure controlling hydraulic valve element, thus making control less responsive. Other types of known electro-hydraulic control valves use springs to urge the main controlled valve element away from its non-neutral positions, or contain a good number of moving parts. Other electro-hydraulic control valves are arranged such that the rate of mechanical movement is dependent on the strength of the magnetic field produced in the control coils. Either of these systems may fall out of balance if the magnetically actuated element becomes permanently magnetized, or if the strength of the signal reaching the control coils becomes out of balance through extended use, or if the springs become fatigued.
In modern aircraft, including jet aircraft and missile type aircraft, a responsive electro-mechnical servo controller is needed to convert movement commands supplied in the form of electrical signals, into mechanical motion for controlling parts of the aircraft, the flight control surfaces being the most notable example. The most desirable characteristics in such a control system include, but are by no means exhaustive, light weight, quick response, fewer moving parts to reduce wear, maximum degree of control and the ability to function in the hostile aircraft environment. Elements of this aircraft environment include extreme heat produced by Aircraft engines which is passed on by conduction and radiation to nearby devices, and gravitational acceleration forces which may affect the performance of moving parts.